This invention relates to a process for the production of moldings based on polyurethanes by reacting organic polyisocyanates with selected polyhydroxyl compounds to form an intermediate product containing free isocyanate and hydroxyl groups which is present in the "B-stage," i.e., an intermediate product which is stable in storage at temperatures below 100.degree. C., more particularly at temperatures below 40.degree. C., solid and capable of being powdered and melted, and subsequently hardening this intermediate product, accompanied or followed by forming a molding.
Solid polyurethanes in the so-called "B-stage," i.e., partial reaction products of organic polyisocyanates and polyhydroxyl compounds, which still contain free isocyanate and hydroxyl groups at room temperature, but which nevertheless, are stable in storage at room temperature or moderately elevated temperature and can only be hardened by the action of heat, have not been known before. On the other hand, intermediate-stage mixtures such as these would represent interesting one-component systems which could be stored at room temperature and hardened at any time by the action of heat.
It has now surprisingly been found that combinations of organic polyisocyanates of the type known from polyurethane chemistry can be reacted with selected polyhydroxyl compounds described in detail hereinafter to form intermediate stages which are stable in storage at from 0.degree. to 40.degree. C., particularly at room temperature, and which still contain free isocyanate and hydroxyl groups, and hence, are capable of being cross-linked under the effect of heat.